Air fresheners are products capable of imparting a desired scent, e.g., fragrance, perfume or deodorant, into the air to give pleasant smells or mask offensive odors. They are often used in a closed area, such as, the interior of an automobile or household. In the household, they are mostly used for the area where unpleasant odors are likely to occur, such as bathrooms, kitchens, bedrooms, living rooms and the like.
Air fresheners have at times been prepared in the form of a paste or gel to control spills or leaks. Most of the air freshener gels commercially available in the market are aqueous-based gels in which colloidal dispersions of droplets of fragrance, such as volatile oily components, are distributed in a hydrocolloid matrix. The main components of such commercially available aqueous gels can often include a fragrance, a surfactant and a co-solvent. The aqueous gel is typically composed of water, a gelling agent and a cross-linking agent, and included in the air freshener gel in an amount of over 80 wt %, or more typically, over 90 wt %. See, for example, US Patent Application Publication No. 2005/0037080. The gelling agent typically includes carageenan, alginate, carboxymethylcellulose (CMC), gelatin or gellan glum. In practical effect, the cross-linking agent can interact with the gelling agent to from a matrix, which immobilizes the largely aqueous medium.
Typical fragrances present in the current products include complex mixtures of fragrant compounds with varying volatility. They are typically included in the air freshener gel in an amount of about 1 to 10 wt %. See, U.S. Patent Application Publication No. 2005/0037080. Top notes, the most volatile part of the fragrance, are often associated with the freshness and the first impression perceived by the customers. Middle notes and bottom notes, which are less volatile components, contribute to the long-lasting scents throughout the gel life time. Thus, the relatively steady emission of the fragrance during the period of use is an important issue for fragrance gels.
With the addition of the surfactant, the oily fragrance is emulsified into tiny droplets. Generally, nonionic surfactants are preferred as they can provide good activity and good gel clarity. Examples for the nonionic surfactants include ethoxylated alkyl phenol, nonyl phenols, ethyoxylated alcohols, and the like. See, U.S. Pat. No. 6,071,506. The clarity is related to the amounts of fragrance and surfactant in the gel composition.
Opaque or cloudy appearance of the gel results from phase separation due to an insufficient emulsification, which makes the gel undesirable for decorative purposes. The phase separation gets more serious and difficult to solve with high fragrance loadings. It may be possible to increase the concentration of the surfactant to reduce or eliminate the phase separation, but this may adversely affect the fragrance-dispersing capability. Moreover, a certain combination of the fragrance and surfactant may bring about clouding of the gel at lower temperatures due to breakdown of the oil-water microemulsion. See, U.S. Pat. No. 6,071,506. Relatively low fragrance loading brings an obvious disadvantage that a large amount of gel is required to provide sufficient scent to the ambient atmosphere. Thus, in the commercially available products, the package of the gel is usually between 50 g and 250 g, mostly between 100 g and 200 g. See, U.S. Patent Application Publication No. 2005/0274817.
The co-solvent used in such commercially available gels is typically a water-soluble compound to enhance the diffusion of the fragrance in the gel matrix, adjust the delivery rate of the fragrance into the surrounding air and improve the consistency of the fragrance release throughout the product lifetime. Co-solvents used most often include, for example, dipropylene glycol, propylene glycol, other glycol ethers, isopropylmyristate, diethyl phthalate, benzyl alcohol, benzyl benzoate, glyceryl triacetate, ethanol, isopropanol, and the like.
Many of the gel compositions and the preparation methods thereof used in the art involve problems in, for example, i) clarity, i.e., opaque or cloudy appearance due to phase separation of the aqueous-based components and the oily fragrance components; ii) fragrance loading, typically with a low loading of 1 to 10 wt % in the gel composition; iii) gel strength, i.e., soft gel texture relating to the interaction of fragrance, surfactant, co-solvent and cross-linking agents; iv) emission, i.e., consistent diffusing into the surrounding air without perceivable diminution; v) heating, typically at 50 to 80° C. to promote the dispersion, which increases the loss due to evaporation in the processing and greater energy consumption; vi) material cost, i.e., expensive gelling agents, cross-linking agents, and surfactants make the manufacturing less economical; and vii) complexity, i.e., the gel comprises many components interacting with each other to make the gel properties more versatile to control.
Several attempts have been made to solve one or more of these problems with air freshener gel preparation and properties. One such attempt resulted in a transparent gel, which is preferred by customers due to its aesthetic appeal. U.S. Pat. No. 5,750,498 teaches a preparation method for a transparent gelatin gel. The gel is prepared with gelatin obtained from bovine bone, bovine hide, pigskin or the like material. The protein in the gelatin is subject to cross-linking by addition of transglutaminase and the like. U.S. Pat. No. 6,071,506 provides another transparent gel composition prepared with a modified polysaccharide gelling agent and cationic cross-linking agent, such as potassium citrate. U.S. Patent Application Publication No. 2002/0039566 describes a preparation method of transparent gels, using a modified polysaccharide gelling agent without cross-linking or chelating agents. However, these transparent aqueous-based gels can incorporate the fragrance only in the amount of about 1 to 15 wt %, preferably less than 10 wt %. In addition, it is required to heat the gel composition to the temperature of 50 to 80° C. for an effective emulsification of the fragrance and the additional oily components.
Dispersion of the fragrance in the gel matrix can be effectively enhanced using anhydrous gels so that higher fragrance loading can be achieved. For example, U.S. Patent Application Publication No. 2005/0274817 describes an anhydrous gel comprising from 3 to 80 wt % of perfume base. To obtain the perfume base, perfume is mixed with cellulose esters, such as, cellulose acetate esters, cellulose acetate propionate and cellulose acetate butyrate. The gel is formed by vigorous stirring of the mixture at 60 to 100° C. and subsequent cooling of the resultant transparent viscous liquid. However, a careful selection of cellulose esters and a control of component concentrations are necessary therein to obtain transparent to slightly cloudy gels. Otherwise, either the esters are not well dispersed in the fragrance bases or the liquid mixture is not solidified upon cooling.
U.S. Patent Application Publication No. 2005/0037080 describes a method to prepare an aqueous-based gel without heating the mixture for fragrance dispersion and gelation. A gel-forming polymer, an added polymer, a gelling agent, a fragrance, a surfactant and water are premixed and preferably stirred at high speed to disperse the fragrance into the aqueous medium. Then, a pH modifier, such as glucono delta lactone, is added into the mixture to induce the linking of the gel-forming polymer to produce the gel. However, the gel contains only about 0.5 to 10 wt % of the fragrance, and the clarity is reported to be moderate to good.
Disinfectants are frequently used in hospitals, dental surgeries, kitchens, and bathrooms to kill infectious organisms. Gas disinfectants, such as sulfur dioxide, glyoxal, iodine, chlorine, malondialdehyde and ammonia, are well-known due to their high efficiency and simple utilization compared to liquid disinfectants. U.S. Pat. No. 4,717,544 uses thermally depolymerizing, solid polymeric aldehydes in this regard. Polyglutaraldehyde can slowly release gas monomers acting as a disinfectant. U.S. Pat. No. 4,883,828 describes adherent and water-resistant polymeric films prepared from liquid disinfectant compositions, which show prolonged germicidal properties of treated surfaces. US Patent Application Publication No. 2006/0094629 describes a cleaning composition comprising a disinfectant, a surfactant and a solvent. However, it is a great challenge to develop an effective and economical method for controlled release of the safe gas disinfectant.
Silicon alkoxide, when reacted with water, is hydrolyzed into silicon hydroxide, which with further reaction with each other and/or unhydrolyzed silicon alkoxide, can form a 3-dimensional silica network in the liquid medium. In addition, colloidal silica suspension can form a 3-dimensional gel framework by condensation. However, application of such an inorganic silica gel or colloidal silica suspension has not been attempted in the prior art in air fresheners or disinfectors.